The present invention relates to a device for feeding fuel to industrial furnaces (including boilers) fired by spreader stokers, fluidized bed combustion, and like technologies, and more particularly to combination mechanical/pneumatic fuel feeders for feeding coal.
Most coal feeders in use today are of the mechanical type using a rotating shaft with blades or paddles, in that they propel the coal into the furnace. Although mechanical coal feeders work adequately, they suffer the disadvantage that they comprise many moving parts which are exposed to the heat of the furnace and often to damaging tramp material, all of which can present maintenance problems. Also, pneumatic systems such as air swept spouts have been in use for years, but principally for incineration of refuse. Typically, the metering device for such systems is remotely located with the refuse fuel free falling through a chute onto the air swept plate. Attempts have been made to mix coal with the refuse at the remote metering location and then letting the mixture free fall together, however such systems have not gained industry acceptance. Combination coal/refuse feeders have been used which consist of a mechanical coal thrower combined with an air swept refuse feeder having remote refuse metering and a free fall chute, using air of variable flow rate to spread the refuse across the furnace grate. Also, coal feeders have utilized steam or compressed air to blow coal off a shelf into a furnace, but these systems did not use a closely coupled metering conveyor, nor did they vary steam or air flow to spread the coal across the furnace to fully cover the grate with fuel. Mechanical rotors, by themselves, have a difficult time throwing very fine coal to the rear of a long furnace. By the same token, air swept feeders have difficulty in feeding coarse coal past the middle of the furnace.
One of the primary objects of the present invention therefore resides in the provision of a combination mechanical/pneumatic coal feeder which provides the pneumatic energy to propel finely sized coal particulate as well as the mechanical energy of a rotor assembly to propel coarser sized coal into the furnace. Such a combination provides improved fuel distribution within the furnace. The present invention therefore obviates the aforesaid problems and provides increased reliability and overall performance.
Other advantages and features will become apparent from the following specification taken in connection with the accompanying drawings.